1. Field of the Invention
The present invention relates to an electro-optical device, particularly to an optical shutter which is usable for the ON/OFF control of blue light.
2. Description of the Prior Art
In a conventional optical shutter which uses a liquid crystal panel, a chiral smectic liquid crystal composition which exhibits ferroelectricity is mainly used, because the speeds of response of a nematic liquid crystal and a cholesteric liquid crystal are low.
Since the value of the optic anisotropy (.DELTA.n) of the chiral smectic liquid crystal composition which exhibits ferroelectricity is around 0.14, it is necessary to limit the thickness (d) of the liquid crystal composition to about as small as 2 .mu.m in order to uniformly transmit all the three primary colors of light. In this way, it is possible to adjust the product (.DELTA.nd) of the value of the optic anisotropy (.DELTA.n) of the liquid crystal composition and the thickness (d) of the liquid crystal composition to around 280 nm. FIG. 3 shows the spectral property exhibited when the product (.DELTA.nd) is 280 nm.
In case that a liquid crystal device which has such a spectral property is used as a blue color shutter, a blue color filter is provided on an optical path so as to constitute the optical shutter in combination with the liquid crystal device.
A first problem in the conventional optical shutter is that if the thickness (d) of the liquid crystal composition is thin, such a high-grade production technique is required that the liquid crystal panel is difficult to produce.
In the case of producing the liquid crystal device as an optical shutter, since two electrodes are provided opposite to each other between two substrates, when an electrically conductive contaminant is included between the two opposed electrodes, an electrical short circuit occurs, which nullifies the function of the liquid crystal device.
On the other hand, if the thickness (d) of the liquid crystal composition is increased to about 3 .mu.m in order to relieve such a problem, although the production technique becomes easier, the transmittance on the short wavelength side of the visible light region is excessively lowered and the blue color is difficult to transmit.
A second problem is that when the color filter which is attached to the liquid crystal device is blue, the transmittance of blue light is poor.
In case that the liquid crystal device which uniformly transmits the three primary colors of the light is used as a blue color shutter, a blue color filter is provided on the optical path so as to constitute the optical shutter in combination with the liquid crystal device. However, since the blue color filter is poor in transmittance even in the vicinity of the blue color wavelength as shown in the spectral sensitivity in FIG. 4, the blue color filter is unsuitable for the use which needs a large amount of light.